This invention relates to a pulp moulding process. More particularly but not exclusively, the invention relates to a pulp moulding process, a pulp moulding system, specific pulp moulding apparatus and a pulp moulded product made by such a process, system and/or apparatus.
The process of pulp moulding in which pulp, typically constituted by water and raw materials such as paper, is moulded to produce products such as functional packaging materials is well known. The process traditionally incorporates the steps of pulp stock preparation, wet forming of products with forming dies, transferring of wet products with transfer dies, drying and packing of the final dry products.
Known disadvantages of the traditional pulp moulding process include relatively high capital costs, poor product quality, high energy costs and high space requirements as well as relatively high manpower requirements.
A known improvement of the traditional pulp moulding process is the so-called xe2x80x9cin-mould dryingxe2x80x9d or xe2x80x9cthermo-formedxe2x80x9d process, the process endeavouring to achieve an improved quality comparable with injection moulded, thermoformed plastic products. The in-mould drying process comprises the traditional process, characterized in that it substitutes the step of conveyor drying with an in-mould drying step wherein the wet or so-called xe2x80x9cin-mouldxe2x80x9d dried product is press dried between heated, opposed, closable pressing tools, with steam resulting from the heating being scavenged under vacuum. The incorporation of the in-mould drying step is aimed at improving poor product finish such as surface coarseness as well as dimensional inaccuracies and deformities. The poor product finish is caused primarily during process, where the wet product is subjected to high temperature, high velocity air flow. In a preferred form, the in-mould drying process includes further in-mould drying in down line pressing stations. The added advantage of additional pressing stations is the speeding up of the pressing portion of the pressing and drying process.
A variation of such in-mould drying processes is found in U.S. Pat. No. 4,088,259 in the name of John T Sutton. U.S. Pat. No. 4,088,259 discloses apparatus for moulding an egg carton wherein a pulp egg carton is formed in a forming mould, transferred to a vacuum drying mould, and carried through several subsequent drying and finish-forming stations.
Known disadvantages of the in-mould drying process however include relatively slower cycle times and corresponding lower product output, relatively high down time due to slower mould changing procedures, expensive tooling, an additionally required vacuum system for steam scavenging and relatively larger sized moulders so as to provide for the additional pressing stations and expensive pneumatic and/or hydraulic pressing system.
It is accordingly an object of the invention to provide a pulp moulding process, a pulp moulding system as well as products moulded from such a process and/or system which will overcome or at least reduce the above disadvantages, or at least to provide a novel and/or relatively inexpensive, alternative pulp moulding process.
According to a first aspect of the invention there is provided a pulp moulding process including the steps of preparing pulp stock; forming wet products by means of a forming die; transferring the wet products from the forming die by means of a heated transferring die-and-heated pressing tool arrangement for in-mould pressing and drying of the wet product; and delivering the dried products to a down line facility.
The process may include the step of using a heated fluid medium for providing heat in the pressing and drying step, the medium being preferably steam.
The process may include the step of using a heated fluid medium for providing heat in the pressing and drying step, the medium being preferably thermal oil. The thermal oil may be maintained at a negative gauge pressure.
The process may include any one or both of the steps of forcing steam generated during the pressing and drying step in one direction through the in-mould wet product; and venting the generated steam to the atmosphere, alternately scavenging the stream under vacuum.
The method may include any one or both of the steps of forcing heated gas, such as air, through the in-mould wet product at high pressure; and venting the steam generated during the in-mould pressing and driving step to the atmosphere, alternatively scavenging the steam under vacuum.
According to a second aspect of the invention there is provided a transfer die-and-heated pressing tool arrangement for use in a pulp moulding process as hereinbefore defined, the transfer die-and-pressing tool arrangement comprising a male part and a female part, at least one part being provided with a primary fluid passage for receiving a heating fluid therethrough and at least one part being provided with at least one vent so as to allow steam generated during an in-mould pressing and drying step to escape therethrough to the atmosphere, alternatively to a vacuum.
The heated transfer die-and-pressing tool arrangement may be characterized in that at least one of the male part and female part may comprise a die element mounted on a plate including a plenum chamber incorporating the primary fluid passage. The heated transfer die-and-pressing tool arrangement may be configured so as to allow the in-mould pressing and drying step to take place with the plate being oriented substantially vertically.
The heated transfer die-and-pressing tool arrangement may be characterized in being provided with at least one secondary fluid passage for receiving pressurized gas, such as air, therethrough, the secondary fluid passage being oriented so as to communicate gaseously with the vent to force the pressurized gas and the steam generated during the in-mould drying step in one direction through the in-mould wet product via the vent directly to the atmosphere, alternatively to a vacuum.
The heated transfer die-and-pressing tool arrangement preferably is provided with a set of secondary fluid passages and a set of vents, the set of secondary fluid passages and the set of vents being staggered relative to each other so as to enhance the substantially uniform flow of pressurized gas through the wet product.
According to a third aspect of the invention there is provided press drying equipment for an in-mould drying, pulp moulding system, the equipment including a heated transfer die and a heated pressing tool, the heated transfer die and the heated pressing tool being operatively associated mechanically with each other so as to provide a heated, mechanical press therebetween in a heated transfer die-and-heated pressing tool arrangement.
The heated transfer die-and-heated pressing tool arrangement may be rotary so as to enable rotary transfer and drying of a wet product between a forming die and a down line facility.
According to a fourth aspect of the invention there is provided a method for in-mould drying of a wet product in a pulp moulding process, the method including the step of passing pre-heated gas, such as air, through an in-mould wet product so as to accelerate the drying of the product.
According to a fifth aspect of the invention there is provided a method of heating a pressing tool in a pulp moulding process, the method including the step of flowing a heating fluid through a fluid passage in a heated pressing tool.
According to a sixth aspect of the invention there is provided an in-mould drying, pulp moulding system comprising means for preparing pulp stock; a wet forming section, incorporating forming dies; and means for transferring wet product from the forming dies and press drying the wet product, the means including a heated transferring die-and-pressing tool arrangement, the arrangement being substantially as hereinbefore defined.
The system may include a down line drying tunnel so as to complete drying, thus enhancing the overall cycle of the system.
According to a seventh aspect of the invention, there is provided a pulp moulded product, manufactured using pulp moulding process including the steps of preparing pulp stock; forming wet products by means of a forming die; transferring the wet products from the forming die by means of a heated transferring die-and-heated pressing tool arrangement for in-mould pressing and drying of the wet product; and delivering the dried products to a down line facility.
A preferred embodiment of the invention well now be described by means of a non-limiting example only and with reference to the accompanying drawings.